Natural Level Widths Research Articles

Direct Determination of Ground-State Transition Widths and Natural Level Widths with the Method of Relative Self Absorption

The method of relative self absorption is based on the technique of nuclear resonance fluorescence measurements. It allows for a model-independent determination of ground-state transition widths, natural level widths, and, consequently, of branching ratios to the ground state for individual excitations. Relative self–absorption experiments have been performed on the nuclei 6 Li and 140 Ce. In order to investigate the total level width for the 0+ 1 , T = 1 level at 3563 keV in 6 Li, a high-precision self-absorption measurement has been performed. In the case of 140 Ce, self absorption has been applied for the first time to study decay widths of dipole-excited states in the energy regime of the pygmy dipole resonance.

Multispace quantum interference in a57Fe synchrotron Mössbauer source

A physical picture for coherent emission of $\ensuremath{\gamma}$ rays by a nuclear array excited with synchrotron radiation is given. The particular case of a pure nuclear Bragg reflection from the ${}^{57}$FeBO${}_{3}$ crystal is analyzed. During free de-excitation of the nuclei, a nuclear exciton polariton is developing inside the crystal and generates at the exit of the crystal a coherent $\ensuremath{\gamma}$-ray beam. In the crystal the nuclear levels of ${}^{57}$Fe are split because of a combined magnetic and electric interaction. The rich picture of $\ensuremath{\gamma}$-ray interference is described, which involves geometrical space, energy, and spin domains. In the vicinity of the N\'eel temperature of the crystal the magnetic splitting of nuclear levels nearly collapses. These conditions lead to drastic changes in the angular, energy, and temporal properties of the emitted radiation. The emission angular function, which in the approximation of a plane incident wave represents the emission intensity for different angular settings of the crystal near Bragg angle, strongly broadens and transforms to a double-hump structure with a central dip between the peaks. The energy and temporal distributions of the emitted radiation crucially depend upon the crystal angular setting. Beyond the central dip, the energy distribution of nuclear scattering acquires a complicated form with several satellites at various energies. In contrast, at the exact angular position of the central dip, the energy spectrum exhibits a single line shape with the line width close to the natural width of the nuclear resonance. The obtained results constitute the theoretical basis for the understanding and for the further elaboration of the ${}^{57}$Fe synchrotron M\ossbauer source---the device that provides a collimated beam of intense and polarized $\ensuremath{\gamma}$ radiation in an energy bandwidth of nanoelectronvolts, the nuclear resonance natural level width.

Angular distribution in the 1 s → 3 p coherently excited resonant KLL Auger spectrum in neon

Angular anisotropies, energies, and relative intensities have been studied for the 1 s → 3 p resonant KLL spectrum in neon. The resonant excitation of the 1 s2 p 22 p 63 p configuration leads to a multiplet of four levels with J = 0, 1, 2, and an energy splitting ≤ 35 meV which is much smaller than the natural level widths of about 250 meV. Thus, the various states of the multiplet are excited (more or less) coherently. To obtain the angular distribution of the Auger lines, knowledge of the density matrix is required. This matrix includes all information about the specific excitation process, whereas the dynamics of the autoionization is described by the relative intensities and Auger angular parameters A 2. Multiconfiguration Dirac-Fock wave functions have been used to calculate this set of coefficients in an intermediate coupling scheme including initial and final state correlations. The use of these data in the interpretation of an angular distribution measurement is briefly discussed.

L3-edge anomalous scattering by gadolinium and samarium measured at high resolution with synchrotron radiation

The anomalous scattering terms f′ and f′′ for Gd and Sm near their L3 absorption edges, measured in diffraction experiments with synchrotron radiation more nearly monochromatic than the natural level widths, show even larger effects than earlier measurements with a larger X-ray bandwidth. A test of angular dependence shows f′ for Sm to decrease in magnitude with increasing diffraction angle, while f′′ is essentially constant.

Angular distribution of electrons from autoionising states with unresolved fine structure

Assuming an unpolarised beam, an unpolarised target and a negligibly small amplitude of the direct ionisation process, the angular distribution of electrons from the decay of autoionising states with an arbitrary ratio between the energy splitting of fine structure levels J, J' and the natural level width Gamma is derived.

Resonant acceptor levels in zero-gap semiconductors under uniaxial stress

The variation with uniaxial stress of acceptor binding energy, as well as the natural level width, are calculated by the resolvent method in the case of zero-gap structures. We have neglected the warping of the ${\ensuremath{\Gamma}}_{8}$ bands and assumed a short-range impurity potential. When the resonant level merges into the induced gap and becomes a perfectly localized state, an anomaly appears in the stress dependence of the binding energy. A phase-shift analysis of the problem is presented, which enables a complete discussion of the nature of the impurity levels in zero-gap semiconductors.

Total and partial atomic-level widths

Total and partial atomic-level widths of the K-, L-, M- , and N -levels of the elements (covering Z up to 120 for K - and L -levels) are presented in graphic form. Graphs are based on theoretical predictions; total widths are natural level widths as governed by the rates of the various deexcitation processes for a single hole in that level. The drawings make possible, throughout the periodic table, a quick survey of the magnitude and trends of the total level widths, rates and yields of radiative, Auger, and Coster-Kronig processes,and widths of x-ray, Auger, and Coster-Kronig lines.

A Study of the (3He, d) Reactions Leading to11C and12C

The reactions 10B(3He, d)11C and 11B(3He, d)12C have been studied, using magnetic analysis, at a bombarding energy of 9.84 MeV. A new level in 11C at 6.345 ± 0.010 MeV excitation was observed. Deuteron angular distributions leading to the ground and first five excited states of 11C were measured, and an attempt has been made to fit these with stripping curves. Absolute proton reduced widths for the 11C levels have been extracted. Using the 11B(3He, d) reaction, the energy levels of 12C between 9 and 15 MeV have been studied. Natural widths of levels at 10.84, 11.82 and 13.38 MeV were measured to be 320, 300 and 700 kev respectively. Stripping analyses of the deuteron angular distributions yielded l-values of 2, 0, 0 and 1 respectively for the states of 12C at 9.63, 10.84, 11.82 and 12.70 MeV. Absolute proton reduced widths and also α-particle reduced widths, from the measured total widths, have been extracted for some levels of 12C.